Often it is desirable to provide two antenna arrays at a wireless communication site. For example, in typical cellular systems there is a need for two transmitter arrays for a single carrier. In order to provide a traffic channel as well as a control channel in a particular service area, cellular providers will typically deploy two standard sector arrays, generally physically spaced apart by an appreciable distance. However, the phase centers of such arrays are offset with respect to one another, which can result in undesirable communication attributes. For example, a pilot signal transmitted from a first such array (having a first phase center) may not experience fading with respect to a particular subscriber unit whereas a corresponding traffic channel transmitted from a second such array (having a second phase center) may experience significant fading.
Moreover, the aforementioned arrays are relatively simple configurations for providing illumination of an associated area, such as a 120° sector. Accordingly, such arrays do not accommodate complex beam forming as is available from a more complex array, such as a phased array configuration. Providing complex beam forming, such as using a phased array configuration, presents implementation challenges. For example, array configurations adapted to facilitate beam forming often have a larger aperture associated therewith and, accordingly, present issues with respect to tower space and wind loading. These issues are compounded when accommodating a two array configuration. For example, two beam forming arrays would occupy a large space on the tower and might incur wind loading conditions that are not supportable by the tower. Moreover, there are additional issues with respect to aesthetics, zoning, etcetera, that make deploying beam forming antenna arrays, and particularly two beam forming antenna arrays, on a tower impractical.
An additional challenge with respect to providing complex beam forming is presented with respect to implementing a control system to facilitate proper beam forming. For example, a dynamic control system may be implemented to monitor attributes with respect to cell morphology and/or topology in order to adjust beam forming parameters. Such adjustment of beam forming parameters may be utilized to optimize antenna beam configurations for communications within a desired area, such as a sector of the cell, and/or to minimize interference with respect to other areas, such as another sector of this or another cell. Systems for providing dynamic control of antenna beams are shown and described in U.S. Pat. No. 6,108,565 entitled “Practical Space-Time Radio Method for CDMA Communication Capacity Enhancement” and U.S. Pat. No. 5,889,494 entitled “Antenna Deployment Sector Cell Shaping System and Method,” the disclosures of which are hereby incorporated herein by reference.
A need exists in the art for systems and methods which provide antenna arrays adapted to facilitate desired beam forming while providing a configuration supporting multiple discrete antenna beams. A need further exists for such multiple discrete antenna beams to be provided with a common phase center. A still further need exists such systems and methods to be adapted to provide a relatively simple and/or inexpensive solution, such as by avoiding the use of dynamic antenna beam control systems.